US6538498B2 - Gm-C tuning circuit with filter configuration - Google Patents
Gm-C tuning circuit with filter configuration Download PDFInfo
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- US6538498B2 US6538498B2 US10/113,600 US11360002A US6538498B2 US 6538498 B2 US6538498 B2 US 6538498B2 US 11360002 A US11360002 A US 11360002A US 6538498 B2 US6538498 B2 US 6538498B2
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- 230000007423 decrease Effects 0.000 claims description 2
- 238000010586 diagram Methods 0.000 description 16
- 239000003990 capacitor Substances 0.000 description 3
- 230000010355 oscillation Effects 0.000 description 3
- 230000035945 sensitivity Effects 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/16—Circuits
- H04B1/26—Circuits for superheterodyne receivers
- H04B1/28—Circuits for superheterodyne receivers the receiver comprising at least one semiconductor device having three or more electrodes
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H11/00—Networks using active elements
- H03H11/02—Multiple-port networks
- H03H11/16—Networks for phase shifting
- H03H11/22—Networks for phase shifting providing two or more phase shifted output signals, e.g. n-phase output
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K9/00—Demodulating pulses which have been modulated with a continuously-variable signal
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/099—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop
- H03L7/0995—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop the oscillator comprising a ring oscillator
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/16—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop
- H03L7/18—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop
- H03L7/197—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop a time difference being used for locking the loop, the counter counting between numbers which are variable in time or the frequency divider dividing by a factor variable in time, e.g. for obtaining fractional frequency division
- H03L7/1974—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop a time difference being used for locking the loop, the counter counting between numbers which are variable in time or the frequency divider dividing by a factor variable in time, e.g. for obtaining fractional frequency division for fractional frequency division
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
- H04B1/403—Circuits using the same oscillator for generating both the transmitter frequency and the receiver local oscillator frequency
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/372—Noise reduction and elimination in amplifier
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H11/00—Networks using active elements
- H03H11/02—Multiple-port networks
- H03H11/04—Frequency selective two-port networks
- H03H2011/0494—Complex filters
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
- H03L7/089—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal the phase or frequency detector generating up-down pulses
- H03L7/0891—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal the phase or frequency detector generating up-down pulses the up-down pulses controlling source and sink current generators, e.g. a charge pump
Definitions
- the present invention relates to a gm-C tuning circuit and method for using same, and in particular to a gm-C tuning circuit using a poly-phase filter.
- a gm-C tuning scheme generally uses a master-slave tuning scheme to adjust a filter frequency that is inversely proportional to gm/C time constant (or RC time constant).
- a master circuit is a copy of a slave block.
- the master circuit receives absolute frequency information from an external oscillator and adjusts transconductance to get the selected filter cut-off frequency.
- the control voltage of a master tuning feedback loop in the master circuit is copied to the slave block to reproduce the adjusted transconductance on the slave block. Then, the slave block becomes a main filter body whose cut-off frequency is controlled by the master circuit.
- FIG. 1 is a diagram that illustrates a master-slave voltage controlled oscillator (VCO) based tuning scheme.
- a master block 110 outputs a control voltage 130 to a slave filter 140 .
- the master circuit 110 includes a comparator 111 , a low pass filter 112 , a rectifier 113 , a voltage-to-current (V-I) converter 115 , a low pass filter 116 that outputs a feedback signal 118 and a master VCO 120 .
- the slave filter 130 is a copy of a master circuit.
- a comparator 111 compares a reference frequency Fref with an output frequency of the master VCO 120 f m .
- the low pass filter 112 low pass filters an output of the comparator to provide the control voltage 130 of the master circuit 110 that is copied to the slave filter 130 .
- the rectifier 113 rectifies the output frequency f m from the master VCO 120
- the V-I converter 115 converts an input voltage from the rectifier 113 and a reference voltage Vref
- the low pass filter 116 receives a converted current from the V-I converter 115 and outputs the feedback signal 118 to the master VCO 120 .
- an oscillation frequency of the master VCO 120 is determined by a time constant of each integrator, that is, the C/gm time constant when the gm-C integrator is used for the master VCO 120 .
- the gm-C VCO based tuning circuit has relatively small hardware requirements and a simple feedback structure.
- the related art gm-C VCO tuning circuit has the disadvantage that a very high Q-factor is required for the VCO oscillation.
- FIG. 2 is a diagram that illustrates another related art master-slave voltage controlled filter tuning scheme.
- a master block 210 includes a comparator 211 , a low pass filter 212 , first and second rectifiers 213 , 214 , a voltage to current (V-I) converter 215 , a low pass filter 216 and a master biquad 220 .
- the master block 210 copies a control voltage 230 to a slave filter 240 .
- the master circuit 210 is a copy of a slave filter 240 .
- the comparator 211 of the master block 210 receives a reference voltage Fref frequency and an output frequency f m from the master biquad.
- the low pass filter 212 receives an output from the comparator 211 and outputs the control voltage 230 to the slave filter 240 and the master biquad 220 .
- the first rectifier 213 receives the output frequency f m from the master biquad 220
- the second rectifier 214 receives the reference frequency Fref.
- the V-I converter 215 receives an output from the first rectifier 213 and the second rectifier 214 , respectively.
- the low pass filter 216 receives an output from the V-I converter 215 and provides a second feedback signal to the master biquad 220 .
- the quality factor of the filter is used for the feedback loop control signal 218 .
- the quality factor of the master circuit 210 must be large enough to provide sufficient sensitivity to phase tuning.
- the large quality factor of the master circuit 210 results in poor matching between the master block 210 and the slave block 240 , which determines accuracy of the master-slave tuning system.
- H LPH of Equation 1A and H BPF of Equation 1B are the Laplace transforms of the low pass filter and the band pass filter, respectively, of FIG. 2 . Substituting the j ⁇ tilde over ( ⁇ ) ⁇ for the Laplace variable s yields.
- FIG. 3 is a diagram that illustrates a related master-slave single integrator tuning scheme.
- a master block 310 copies control voltage 330 to a slave filter 340 .
- the master block 310 is a copy of the slave filter 330 .
- the master block 310 includes a first rectifier 313 , a second rectifier 314 , a voltage to current (V-I) converter 315 , a low pass filter 316 and a single integrator 320 .
- V-I voltage to current
- the first rectifier 313 receives an output frequency f m from the single integrator 320
- the second rectifier 314 receives a reference frequency Fref.
- the V-I converter 315 receives output signals from the first rectifier 313 and the second rectifier 314 .
- the low pass filter 316 receives output from the V-I converter 315 to output the control voltage 330 to the slave filter 340 and as a feedback signal 318 to the single integrator 320 .
- the related art master-slave single integrator tuning scheme uses gm-C integrator 320 as the master of tuning to overcome various problems associated with the VCO type tuning scheme and the VCF type tuning scheme described above.
- the gm-C integrator 320 operates as a capacitor equivalent.
- the amplitude of the gm-C integrator 320 output and that of the input Fref are compared using the rectifier 313 , 314 and the V-I converter 315 .
- the input of the gm-C integrator 320 comes from an external oscillator and an output comes from an Operational Transconductance Amplifier (OTA) cell, which causes inaccurate tuning results.
- OTA Operational Transconductance Amplifier
- An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
- Another object of the present invention is to provide a master-slave circuit not limited by frequency or Q-factor requirements.
- Another object of the present invention is to provide a master-slave tuning circuit using a poly-phase filter.
- Another object of the present invention is to provide a master-slave gm-C poly-phase filter having the same electrical characteristics for a first filter and a second filter compared in the master-slave filters.
- Another object of the present invention is to provide a gm-C poly-phase filter having output signals from high and low pass filters provided by the same circuit.
- Another object of the present invention is to provide a master-slave tuning circuit having increased accuracy.
- Another object of the present invention is to provide a more robust master-slave tuning circuit with increased accuracy and a simplified configuration.
- a tuning circuit that includes a slave filter block that receives a first control signal and outputs a second control signal, and a master filter block that receives first and second prescribed reference signals and outputs the first control signal to the slave filter block, wherein the master filter block includes a polyphase filter that receives the first control signal, a first rectifier coupled to the polyphase filter, a second rectifier coupled to the polyphase filter, and a converter coupled to the first and second rectifiers that outputs the first control signal.
- a tuning circuit that includes a slave filter block having a cut-off frequency that receives a first control signal and outputs a second control signal, and a master filter block comprising a polyphase filter that receives first and second prescribed reference signals and outputs the first control signal to the slave filter block, wherein the second prescribed reference signal has a frequency approximately equal to the cut-off frequency of the slave filter block.
- a tuning circuit that includes a slave filter block having a cut-off frequency that receives a first control signal and outputs a second control signal, and a master filter block that receives the first control signal, the master filter block comprising a high pass filter and a low pass filter, the master filter block adapted to receive first and second prescribed reference signals and output the first control signal to the slave filter block, wherein the second prescribed reference signal has a frequency approximately equal to the cut-off frequency of the slave filter block.
- a method for tuning a master-slave tuning circuit that includes slave filtering a first control signal to output a second control signal, and master filtering first and second reference signals to output the first control signal for the slave filtering, wherein the master filtering includes high pass filtering the second reference signal using a first polyphase filter based on the first control signal, low pass filtering the second reference signal using a second polyphase filter based on the first control signal, rectifying at least one high pass filtered signal and at least one low pass filtered signal, wherein the second prescribed reference signal has a frequency approximately equal to a cut-off frequency of the slave filtering, and converting rectified high and low pass filtered signals to output the first control signal.
- FIG. 1 is a diagram that illustrates a related art master-slave tuning circuit
- FIG. 2 is a diagram that illustrates another related art master-slave tuning circuit
- FIG. 3 is a diagram that illustrates yet another related art master-slave tuning circuit
- FIG. 4 is a diagram that illustrates a preferred embodiment of a master-slave tuning circuit according to the present invention
- FIG. 5 is a diagram that illustrates a preferred embodiment of a rectifier
- FIG. 6 is a diagram that illustrates a preferred embodiment of a voltage-to-current converter
- FIG. 7 is a circuit diagram that illustrates an exemplary transconductance amplifier
- FIG. 8 is a diagram that illustrates a preferred embodiment of an RF communications system.
- FIG. 4 is a diagram that illustrates a preferred embodiment of a master-slave gm-C tuning circuit in accordance with the present invention.
- a master block 410 copies a control voltage 430 to a slave filter 440 .
- the master block includes a first rectifier 413 , a second rectifier 414 , a voltage-to-current (V-I) converter 416 and a gm-C poly-phase filter 420 .
- V-I voltage-to-current
- the rectifier 413 receives high pass filter output signals 425 A, 425 B from the filter 420 and the rectifier 414 receives low pass filter output signals 429 A, 429 B from the filter 420 .
- the V-I converter 416 receives output from the rectifiers 413 , 414 and outputs the control voltage 430 to the slave filter 440 .
- the gm-C poly-phase filter 420 includes transconductance amplifiers 422 , 424 , 426 , 428 . Positive and negative input ports of transconductance amplifier 422 receive a common mode reference signal. A positive output port of transconductance amplifier 424 is coupled to a negative output port of the transconductance amplifier 422 and a negative input port of the transconductance amplifier 424 . A negative output port of the transconductance amplifier 424 is coupled to a positive output port of the transconductance amplifier 422 and a positive input port of the transconductance amplifier 424 .
- the positive and negative output ports of the transconductance amplifier 424 are output nodes for the high pass filtered (HPF) output signals 425 B, 425 A, respectively.
- positive and negative input ports of the transconductance amplifier 426 are coupled to receive a reference input signal 450 .
- a positive output port of a transconductance amplifier 428 is coupled to the negative output port of the transconductance amplifier 426 and a negative input port of the transconductance amplifier 428 .
- a negative output port of the transconductance amplifier 428 is coupled to a positive output port of the transconductance amplifier 426 and a positive input port of the transconductance amplifier 428 .
- the positive and negative output ports of the transconductance amplifier 428 are output nodes for the low pass filtered (LPF) output signals 429 B, 429 A, respectively.
- the filter 420 includes a high pass filter circuit 420 A and a low pass filter circuit 420 B.
- the reference signal 450 is coupled to the positive and negative output ports of the transconductance amplifier 424 through capacitors 423 B and 423 A, respectively.
- Capacitors 427 A and 427 B are coupled between a ground voltage and the negative and positive output terminals of the transconductance amplifier 428 .
- a diagram that illustrates an equivalent circuit 460 of the gm-C poly-phase filter 420 is shown in FIG. 4 .
- the transconductance amplifiers 426 , 428 receives the feedback loop control signal Vctrl as a control signal and respectively outputs the control signal Vctrl to the transconductance amplifiers 422 and 424 .
- the sine wave is preferably used a reference signal. As shown in FIG. 4, a 4 MHz sine wave is used as the reference signal to set the filter 420 cut-off frequency.
- transconductance values increase and the amplitude of the LPF output signals 429 A, 429 B increase and the amplitude of the HPF output signals 425 A, 425 B decrease.
- the rectifiers 413 , 414 preferably detect peak levels of the HPF and LPF output signals respectively, for the comparison.
- the V-I converter 416 receives the rectified outputs from the rectifiers 413 , 414 and generates a pumping current that is preferably proportional to the difference of the amplitude of the rectified output.
- a master block such as the master block 410 according to the preferred embodiments can be adapted as a tuning circuit for various types of transconductance amplifiers.
- An exemplary transconductance amplifier is illustrated in FIG. 7 .
- the transconductance amplifiers in the high pass filter section and the low pass filter section of the master block 410 preferably provide a similar function of operating as resistor-equivalent whose value is 1/gm ohm.
- the common mode reference signal is preferably a DC voltage whose value is about halfV DD (e.g., 1 ⁇ 2 the supply voltage).
- a sine wave is the preferred reference signal 450 , however, alterative types of signals can be used such as a triangular wave can be applied.
- the frequency of the reference signal 450 is preferably applied according to the required cut-off frequency of corresponding slave block. For example, if the cut-off frequency of slave filter is 6 MHz, 4 MHz sine wave should be replaced with 6 MHz sine wave.
- FIG. 5 is a diagram that illustrates a preferred embodiment of a rectifier according to the present invention.
- a rectifier 500 includes PMOS type transistors 501 , 502 coupled in parallel between node A and a ground voltage. Gate electrodes of the PMOS transistors 501 and 502 respectively receive an input signal IN and an input signal complement INB.
- PMOS type transistor 503 is coupled between a source voltage V DD and node A, and PMOS type transistor 504 is coupled between the source voltage V DD and node B.
- Gate electrodes of the PMOS transistors 503 and 504 receive a bias voltage V Bias .
- a fifth PMOS type transistor 505 is coupled between node B and the ground voltage.
- An operational amplifier has an inverting terminal coupled to node B, a non-inverting terminal coupled to node A and an output coupled to the gate electrode of the PMOS type transistor 505 to provide an output signal of the rectifier 500 .
- the rectifier 500 can be used as the rectifier 413 , 414 in FIG. 4 .
- FIG. 6 is a diagram that illustrates a preferred embodiment of a V-I converter 600 according to the present invention.
- transistors 601 and 602 are coupled in series between a power source voltage V DD and the ground voltage.
- transistors 603 and 604 are coupled in series between the source voltage V DD and the ground voltage by commonly coupled drain electrodes that provide an output signal of the V-I converter 600 .
- Transistors 605 and 606 are coupled in series between the source voltage V DD and a current source I s , which is coupled to the ground voltage.
- Transistors 607 and 608 are coupled in series between the source voltage V DD and the current source I S by commonly coupled drain electrodes.
- gate electrodes and the drain electrode of the transistor 605 are coupled together and to the gate of the transistor 601 .
- a gate electrode and the drain electrode of the transistor 607 are coupled together and to the gate electrode of the transistor 603 .
- Gate electrodes of the transistor 606 and 608 respectively receives input signals 620 and 622 , respectively.
- the converter 600 can be used as the V-I converter 416 in FIG. 4 .
- FIG. 8 is a diagram that illustrates a preferred embodiment of an RF communications system used to generate a baseband signal output 880 .
- the RF communications system includes: an RF section 810 coupled to receive an input RF signal 850 ; a baseband section 820 coupled to the RF section 810 to receive corresponding baseband signals 860 from the RF section 810 ; a phase locked loop 830 coupled to the RF section 810 ; and a tuning circuit 840 .
- the tuning circuit 840 outputs a control signal 870 to the baseband section 820 , and includes a master block 410 and a slave block 440 as described above.
- the preferred embodiment of the master-slave tuning circuits and methods of using same according to the present invention have various advantages.
- the control voltage of a feedback loop e.g., Vctrl
- both the master and slave circuits use a gm-C filter.
- electrical characteristics including for example common load level, loading capability should be matched.
- High-pass and low-pass filter portions of a poly-phase filter in the poly-phase filter according to the preferred embodiments use the same filter with different configurations. Further, output signals of the high and low pass filtering come from the same circuits so that both signals have the same electrical characteristics, which result in a more accurate tuning circuit relative to the related art tuning circuits.
- the preferred embodiment of gm-C poly-phase filter tuning circuit provide a simpler circuit configuration for both the master and slave filter bodies.
- the preferred embodiments of a tuning circuit provide an increased robust operations relative to the VCO type related art tuning circuits due to elimination of disadvantages caused by the difficulty of oscillation and to high Q-factor requirements of the VCO type tuning circuits.
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Priority Applications (1)
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US10/113,600 US6538498B2 (en) | 1998-07-24 | 2002-04-02 | Gm-C tuning circuit with filter configuration |
Applications Claiming Priority (5)
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US09/121,601 US6335952B1 (en) | 1998-07-24 | 1998-07-24 | Single chip CMOS transmitter/receiver |
US09/121,863 US6194947B1 (en) | 1998-07-24 | 1998-07-24 | VCO-mixer structure |
US16487499P | 1999-11-12 | 1999-11-12 | |
US09/709,310 US6404277B1 (en) | 1998-07-24 | 2000-11-13 | Gm-C tuning circuit with filter configuration |
US10/113,600 US6538498B2 (en) | 1998-07-24 | 2002-04-02 | Gm-C tuning circuit with filter configuration |
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US09/709,310 Continuation US6404277B1 (en) | 1998-07-24 | 2000-11-13 | Gm-C tuning circuit with filter configuration |
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US20020135417A1 US20020135417A1 (en) | 2002-09-26 |
US6538498B2 true US6538498B2 (en) | 2003-03-25 |
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US09/121,863 Expired - Lifetime US6194947B1 (en) | 1998-07-24 | 1998-07-24 | VCO-mixer structure |
US09/709,310 Expired - Lifetime US6404277B1 (en) | 1998-07-24 | 2000-11-13 | Gm-C tuning circuit with filter configuration |
US10/113,600 Expired - Lifetime US6538498B2 (en) | 1998-07-24 | 2002-04-02 | Gm-C tuning circuit with filter configuration |
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US09/121,863 Expired - Lifetime US6194947B1 (en) | 1998-07-24 | 1998-07-24 | VCO-mixer structure |
US09/709,310 Expired - Lifetime US6404277B1 (en) | 1998-07-24 | 2000-11-13 | Gm-C tuning circuit with filter configuration |
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US6529047B2 (en) * | 2000-12-21 | 2003-03-04 | Intersil Americas Inc. | Mixer driver circuit |
US6542019B1 (en) * | 2001-11-28 | 2003-04-01 | Berkäna Wireless, Inc. | Highly linear and low noise figure mixer |
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US6838929B2 (en) * | 2002-05-07 | 2005-01-04 | Xignal Technologies Ag | Integrated circuit arrangement comprising an active filter and a method for tuning an active filter |
US20040085123A1 (en) * | 2002-05-07 | 2004-05-06 | Gerhard Mitteregger | Integrated circuit arrangement comprising an active filter and a method for tuning an active filter |
US20070019113A1 (en) * | 2002-12-19 | 2007-01-25 | Jan Van Sinderen | Mixer system with amplitude-, common mode- and phase corrections |
US20050062524A1 (en) * | 2003-09-12 | 2005-03-24 | Hidetaka Kato | Transconductance-adjusting circuit |
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US20050122161A1 (en) * | 2003-12-03 | 2005-06-09 | Takashi Fujimura | Active filter circuit using gm amplifier, and data read circuit, data write circuit and data reproducing device using the same |
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US20070057719A1 (en) * | 2005-01-06 | 2007-03-15 | Fujitsu Limited | Analog filter circuit and adjustment method thereof |
US7245178B2 (en) | 2005-01-06 | 2007-07-17 | Fujitsu Limited | Analog filter circuit and adjustment method thereof |
US20070046368A1 (en) * | 2005-08-26 | 2007-03-01 | Cypress Semiconductor Corporation | Circuit for creating tracking transconductors of different types |
US7642845B2 (en) * | 2005-08-26 | 2010-01-05 | Cypress Semiconductor Corporation | Circuit for creating tracking transconductors of different types |
US20070100927A1 (en) * | 2005-11-03 | 2007-05-03 | Samsung Electronics Co., Ltd. | Wide tunable polyphase filter with variable resistor and variable capacitor |
US20080106329A1 (en) * | 2006-11-02 | 2008-05-08 | Seung-Sik Lee | Apparatus for adjusting frequency characteristic and q factor of low pass filter and method thereof |
US7564301B2 (en) * | 2006-11-02 | 2009-07-21 | Electronics And Telecommunications Research Institute | Apparatus for adjusting frequency characteristic and Q factor of low pass filter and method thereof |
Also Published As
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---|---|
US20020135417A1 (en) | 2002-09-26 |
US6194947B1 (en) | 2001-02-27 |
US6404277B1 (en) | 2002-06-11 |
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